Freezing of anisotropic spin clusters in La1.98Sr0.02CuO4

Abstract

A spin-glass compound, La${}_{1.98}$Sr${}_{0.02}$CuO${}_4$, shows quasi-three-dimensional magnetic ordering below $\sim$40 K. A remarkable feature is that the magnetic correlation length along the orthorhombic $a{}_{\mathrm{ortho}}$ axis is much longer than that along the $b{}_{\mathrm{ortho}}$ axis, suggesting that the spin structure is closely related to the diagonal stripe structure. The spin-glass state can be expressed as a random freezing of quasi-three-dimensional spin clusters with anisotropic spin correlations ($\hat{I}{¾}_a^{\prime }\sim 160$ à , $\hat{I}{¾}_b^{\prime }\sim 25$ à , and $\hat{I}{¾}_c^{\prime }\sim 4.7$ à at 1.6 K). The new magnetic state is important as an intermediate phase between the three-dimensional antiferromagnetic ordered phase in La${}_2$CuO${}_4$ and the incommensurate phase in La${}_{1.95}$Sr${}_{0.05}$CuO${}_4$ in which the positions of the incommensurate peaks are rotated by 45${}^{\circ }$ in reciprocal space about ($\ddot{I}€$,$\ddot{I}€$) from those observed in the superconducting La${}_2$CuO${}_4$ compounds.

7 pages, RevTex, 8 PS figures, submitted to Phys. Rev. B